Separation and preconcentration of La from monazite, followed by determination using nondestructive γ-ray spectrometry

Abstract

A method was developed for separation, preconcentration, and determination of La by its radioactive isotope 138 La using an HPGe detector. The method was checked by comparison with ICP-MS. The detection limit (minimum detection activity) is 1.46 and 1.52 Bq kg -1 at 788.4 and 1435.8 keV lines, respectively. The Th(IV) and U(VI) are separated by precipitation. To separate Ac(III), it is extracted jointly with REEs from 0.1 M HNO 3 with HDEHP and then stripped with 0.2 M HNO 3 , with REEs remaining in the organic phase. Lanthanum in a mixture with REEs is determined by γ-ray spectrometry.Monazite ore, rich in REE, Th, and U, is of particular importance for industrial exploitation. The major components of this mineral are La 2 O 3 (33.95%), Ce 2 O 3 (17.10%), ThO 2 (5.5%), Nd 2 O 3 (26.68%), and U 3 O 8 (0.52%) [1][2][3]. According to other data [4,5], Egyptian monazite contains 64.00% REE oxides, 6.04% ThO 2 , and 0.48% U 3 O 8 . REEs find growing use as fine chemicals in modern industry (metallurgy, oil refinery, glass, ceramics, electronics, nuclear engineering) and in high-tech applications (semiconductors, superconductors, optics, lasers) [6]. Determination of lanthanum in monazite [7][8][9][10][11] was based on the monazite breakdown by acid and alkali digestion; the composition of the concentrates and their effect on solvent extraction processes were discussed. Eyal [12] studied the relative dissolution rates and leaching of monazite in a bicarbonate-carbonate solution. Olander and Eyal [13] monitored the interaction of three natural monazite specimens with a bicarbonate-carbonate solution for up to 6.8 years. In this paper, the separation method is based on precipitation to remove Th(IV) and U(VI) and on solvent extraction to separate Ac from REEs. Lanthanum is determined by γ-ray spectrometry using two lines (788.4 and 1435.8 keV) of 138 La (natural abundance 0.09%, T 1/2 = 1.05 × 10 11 years).Several methods have been used for the quantification of REEs in monazite [7,14]. However, these techniques have certain drawbacks. For instance, the detection limit of α-ray spectrometry is often 100-1000 times lower than in γ-ray spectrometry [15,16]. Other drawbacks are low throughput and incremental interference due to matrix effects.